Three linked autosomal loci were studied in smurfs. Pure breeding pink, happy, t
ID: 87488 • Letter: T
Question
Three linked autosomal loci were studied in smurfs. Pure breeding pink, happy, tall smurfs were mated to pure breeding blue, gloomy, dwarf smurfs. The F_1 were testcrossed and the testcross progeny are given below. Determine the order of the loci and the map distances between adjacent loci. Then label the map below. Round your map distances properly to two decimal digits. When labeling the loci on the map, the two outside loci must be in alphabetical order. For example, if you have the following loci: Albinism, Bone length, Cranial size, and Albinism is in the center, you would label the map Bone length - Albinism - Cranial size.Explanation / Answer
Let, the genotype of pure breeding pink, happy and tall smurfs be PPggTT. They produce single type of gametes with PgT genotype.
Let, the genotype of pure breeding blue, gloomy and dwarf smurfs be ppGGtt. They produce single type of gametes with pGt genotype.
So, the genotype of F1 is PpGgTt. They were test crossed. Test cross is a cross between F1 and recessive pure line.
PpGgTt x ppggtt
In this cross, ppggtt produces single type of gamete with all recessive alleles (i.e., pgt).
PpGgTt produces 8 different types of gametes. Phenotype of the off springs is exclusively determined by the gamete from this parent. Gamete from ppggtt parent is irrelevant in phenotype of the off spring.
I have modified table to show all phenotypes.
Phenotype
Gamete from F1 parent
Cross over type
Number Observed
Pink, happy, tall
PgT
Parental
399
Blue, gloomy, dwarf
pGt
Parental
401
Pink, gloomy, tall
PGT
Single crossover
64
Blue, happy, dwarf
pgt
Single crossover
59
Blue, happy, tall
pgT
Single crossover
85
Pink, gloomy, dwarf
PGt
Single crossover
92
Blue, gloomy, tall
pGT
Double crossover
9
Pink, happy, dwarf
Pgt
Double crossover
5
Here, PgT and pGt are parentals (Parentals are more in number than others). Both parentals are reciprocals.
Pgt and pGT are double crossovers (Double crossovers are very low in number than others). Both double crossovers are also reciprocals.
The difference between parentals and double cross overs is middle gene only.
PgT and Pgt are parent and corresponding double cross over, respectively. The difference between them is T gene.
pGt and pGT are parent and corresponding double cross over, respectively. The difference between them is T gene.
So, the middle gene is T gene. Gene order is PTG.
So, I am further modifying the table to include the correct order of the genes.
Gamete from F1 parent
Cross over type
Number Observed
PTg
Parental
399
ptG
Parental
401
PTG
Single crossover (between T and G)
64
Ptg
Single crossover (between T and G)
59
pTg
Single crossover (between P and T)
85
PtG
Single crossover (between P and T)
92
pTG
Double crossover
9
Ptg
Double crossover
5
Distance between P and T = Cross overs between P and T x 100 / total progeny
= (85+92+9+5) x 100 / 1114
= 191 x 100 / 1114
= 17.15%
Distance between T and G = Cross overs between T and G x 100 / total progeny
= (64+59+9+5) x 100 /1114
= (137 x 100) / 1114
=12.3%
1% crossover is equal to 1 map unit and it is also equal to 1 centiMorgan unit.
There are drop down option in the question. Those options are not visible and are not given separately in the question.
Anyway following information will be use filling the answers.
Distance between G and T is 12.30 cM
Distance between T and P is 17.15 cM
Distance between G and P = 12.30+17.15 = 29.45 cM approximately.
Phenotype
Gamete from F1 parent
Cross over type
Number Observed
Pink, happy, tall
PgT
Parental
399
Blue, gloomy, dwarf
pGt
Parental
401
Pink, gloomy, tall
PGT
Single crossover
64
Blue, happy, dwarf
pgt
Single crossover
59
Blue, happy, tall
pgT
Single crossover
85
Pink, gloomy, dwarf
PGt
Single crossover
92
Blue, gloomy, tall
pGT
Double crossover
9
Pink, happy, dwarf
Pgt
Double crossover
5
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